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D—TEXTILES; PAPER

D21—PAPER-MAKING; PRODUCTION OF CELLULOSE

D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR

D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution

The invention relates to the precipitation of starch upon fibers used in the manufacture of paper. It is of particular value in connection with the use of starch in the furnish.

The word starch as used herein, is imtended to include not only the various kinds of starch proper, such as corn starch, potato starch, tapioca starch, etc., or flours containing said starches, but also degradation products such as so-called modified starches, oxidized starches, starch gums, etc.

The advantage due to the use of starch in the manufacture of paper has long been recognized. Starch in various ways has been employed in the coating or finishing of the paper Web after the formation of the latter on the wire. Various proposals have also been put forward for incorporating starch in the furnish, before formation of the web, but it has been found that where a considerable quantity of starch is supplied to the furnish, only a relatively small amount of such starch is found in the formed web. This apparently is due to the fact that starch, being a dispersible colloid, is not precipitated upon or retained by the fibers in' any large amount and, therefore, to a large extent, is retained by, and is carried off with, the white water which drains out of the web. As a result, it has not been possible by ordinary methods to incorporate starch with the web in an 4 amount exceeding a few per cent of the weight of fiber on the dry basis. Also, in order to secure the retention of such relatively small percentage of starch, it has been necessary to use in the furnish a much greater percentage, thereby causing such waste and expense that, practically speaking, the use of starch heretofore in the furnish has been attended with no substantial commercial advantage.

In the co-pending application of one of us,

Rowland, Serial No. 726,125, filed May 17, 1934,

convenience and with substantially no modification of the standard paper plant setup.

We have found that when ordinary starches are added dry and uncooked to the beater, they are too tough to be broken up by the Jordan, whereas if they are cooked to any appreciable extent they are too soft and are dispersed by the Jordan beyond the limits of possible precipitation and, therefore, are ineffective as siz,-

' ing agents if introduced into the process at this After extensive investigation, we have discovered that especially treated starches which are considerably tougher than ordinary or natural starches function perfectly as sizes when introduced into the beater. The beating operation, instead of destroying or reducing the value of said starches as in the case of ordinary starches, seems to condition them and place them in such a state of dispersion as to produce their optimum sizing effect.

In accordance with our special starch treatment, the starch granules are toughened to the extent that they will not be as readily dispersed when they are gelatinized or swollen, for example, by means of boiling water or caustic solution, as ordinary boiled starch. Our special starch treatment may be carried out to the extent that the starch granules will be so toughened that they will not swell or gelatinize in water even when subjected to prolonged boiling temperatures, or such treatment may be carried only to the extent that a slight toughening of the starch granules will be effected, in which latter case the starch granules can be dispersed by means of hot water or caustic solution, but to a substantially lesser degree than untreated starch.

Starch treated in accordance with our invention, when cooked in water and alkali will form a suspension of swollen starch granules which can be readily precipitated by the addition of sufficient acid or acid salt to reduce the pH to about or less. Such precipitated starch can again be brought into a state of suspension by the addition of a sufllcient amount of alkali to bring the aqueous medium to a pH of about or above.

Example The furnish may consist of soda pulp or sulphite pulp, or rag stock, or a combination of the same, and may include also a substantial perfurnish. In fact, the invention appears to work well with almost any kind of furnish used in the manufacture of paper. I

The special starch utilised in our invention may be prepared in the following manner:

1,200 pounds of powdered corn or other raw starch is placed in a steam jacketed mixer, preferably equipped with a power-driven agitator. While the starch is being agitated a mixture of 2,600 cc. of 40 per cent formaldehyde solution, 1,500 cc. of 56 per cent acetic acid. and 4,500 cc. of water are sprayed in and the total mass is mixed for about a half hour, or until the liquid ingredients have been thoroughly incorporated with the starch. At the end of this time, steam at about 50 pounds pressure is turned into the jacket of the mixer and the material is heated for a period of one to two hours or until control tests show the desired degree of action on the starch has taken place. The starch is then dumped out of the mixer and allowed to cool, after which it is ready for use.

A somewhat different method of treating the starch which gives the same desirable results is as follows:-

1,000 pounds of starch is mixed with 1,200 pounds of water in a suitable tank equipped with an agitator. To this mixture is added 10,000 cc. of 40 per cent formaldehyde and 2,000 cc. of 18 Be. hydrochloric acid, and the mass is held at a temperature of about 75' I". and agitated for about v24, hours, or until control tests show that the desired degree of action on the starch has taken place. At the end of this time, the water is separated from the starch by means of a filter dryer. It is-then ready for use.

The control tests referred to above are such as will show that the starch, after the above treatment, will swell in hot water or in a caustic solution to form a suspension or gel but will be reprecipitated by acid. The following comparative tests will illustrate certain properties of our special'starch as compared with ordinary starch.

Ten grams each of ordinary corn starch and our treated corn starch are cooked up separately with 150 cc. of water and .01 grams of caustic soda to a temperature of 195 1''. and held at this temperature for 15 minutes. A 20-gram portion is taken from each of these cooked samples of gelatinized starch and dispersed in 210 cc. of distilled water. The subsequent starch suspensions are poured into 250 cc. graduates and placed side by side. The pH of these dispersed starches will be about 12.0. To each of the graduates is then added 6 cc. of 1/10 N. sulphuric acid and distributed by shaking in the graduate. Immediately after the acid is added to the dispersion of the treated starch a iiocculent precipitate of starch forms and begins to settle out; whereas in the case of the ordinary corn starch dispersion there is no noticeable precipitation. The pH of the starch dispersion after the addition of the acid is approximately 3.0.

It should be understood that the above methods are merely specific examples of how we treat the starch to obtain the dmired degree of modification and that we do.not wish to limit ourselves to these specific examples of treatment. The acid'ingredient used in the above examples is merely a catalyst and as such accelerates the reaction between the formaldehyde and the starch and enables the use of smaller amounts of formotherwise bepracticab.

Intheseeondmethodoftreatmentpractically' any water soluble acid can be med as the catalyst.

Our special starch is prepared for use as follows: A suitable quantity of water corresponding to 15 times the weight of the starch iswarmed to a temperature of between 56' and C. The dry starch is then put into the water and stirred until-the lumps are thoroughly wetted out. A quantity of alkali such as sodium hydroxide in any concentration, preferably around 20 per cent in water and amounting to 7.3 pounds of dry caustic per 100 pounds of starch being treated, is introduced into the starch mixture with stirring. As soon as it has been thoroughly stirred in, the agitation may be discontinued and the batch allowed to stand for from 10 to minutes, during which interval the starch swells into a gelatinous condition and becomes quite thick and at" first white and opaque. but in a few minutes transparent and glassy. It is then ready for addition to the beater. This condition of alkalinity in the starch solution will generallyv render the beater contents appreciably alkaline. Rosin size may be introduced, as well as other ingredients of the furnish, toward the end of the beating cycle to prevent foaming, although ommill experience with this procedure has not as yet presented a foaming problem. Alum, which is the remaining addition to effect precipitation of the starch and also of the rosin size, is withheld until the furnish has passed through the Jordan and there it may be added tobring the furnish acidity down to any pH preferred by the mill,

which is usually a pH necessary for effective rosin sizing. We have" added the alum at difierent points at different mills, and find that it is immaterial at what point weadd it so long as it is thoroughly mixed in.

While in our preferred practice the alum is'introduced between the Jordan and the paper machine, satisfactory results may be obtained if the alum is added to the beater immediately following the introduction of the starch and rosin. Since, when starches of the special type herein considered are used,' precipitation will not occur until after the furnish has passed through the Jordan and the starch has become broken down, in case the alumina has previously been formed in the beater, it would be immediately available to effect precipitation at the moment the starch is broken down in the Jordan.

The furnish prepared as described above is run through the'paper machine in the ordinary manner without any material change in the machine practice.

Paper made according to the process described to the extent indicated by the appended claims,

which are to beinterpreted as broadly as the state of the art will permit.

We claim as our invention:

1. The improvement in the art of paper-making, which comprises introducing into the furnish before the completion of the beating operation an alkaline dispersion of a tough, formaldehyde treated raw starch which is capable of being colloidally dispersed by the'beating action and will retain after such beating its ability to be precipitated on the fiber, and, prior to the paper-forming operation, adding alum to the furnish so as to precipitate said starch upon the fiber in finelydivided form.

2. The improvement in the art of paper making, which comprises introducing into the furnish, before the completion oi the beating operation, an alkaline dispersion of a tough starch produced by treating a raw starch with formaldehyde and, prior to the paper-making operation, adding sufllcient acidic material to the i'urnish to precipitate said starch upon the fiber in finely-divided form.

3. The improvement in the art of paper making, which comprises introducing into the furnish, before'the completion of the beating operation, an alkaline dispersion of a tough starch produced by treating a'raw starch with formaldehyde and an acid catalyst and, prior to the paper-making operation, adding sumcient alum to the furnish to precipitate said starch upon the fiber in finelydivlded form.

4. The improvement in the art of paper-mak-- ing, which comprises introducing into the furnish before the completion oi the beating operation an alkaline dispersion of a tough, formal ehyde treated raw starch which is capable of b ng colloidally dispersed by the beating action and will retain after such beating its ability to be precipitated on the fiber, and precipitating said starch upon the fiber by the addition of acidic material.

5. The improvement in the art of paper-making, which comprises introducing into the furnish, before the completion of the beating operation, an alkaline dispersion 01' a tough starch produced by treating a raw starch with formaldehyde and an acid catalyst and, prior to the paper-making operation, adding sufllcient acidic material to the furnish to precipitate said starch upon the fiber in finely divided-form.